A system described in copending patent application 07,714,250 filed 11 June 1991 for isolating a dump sitting on the ground has three different structures which ar installed under the dump sequentially, as needed. The first structure includes a tunnel driven longitudinally through the ground underneath the dump and an array of drainage pipes passing through the ground and each having a lower end opening into the tunnel and an upper end at the surface. The second structure includes a water barrier in the ground around at least some of the drainage pipes. The third structure includes a water-impervious mass of backfill in a slit underneath the barrier and having a lower end at the tunnel and an upper end at the surface. Unpublished and withdrawn German patent application 4,018,821 describes a system where drainage in such a dump-protection installation is assisted by providing a compressed-air arrangement for keeping the perforations in the drainage pipe clear. Such a system is used in order to prevent blockages of the drainage pipe from rendering the installation useless or requiring that it be dug up and serviced and/or replaced.
The main problem with the known solutions is that they require that expensive mining techniques be applied to install them. The necessary tunnels and slits must be driven and cut by equipment that is expensive to own and operate. Instead of using spoil cut from the face as backfill, special water impervious fill must be moved into the job, along with the requisite vapor-barrier foils. These procedures are necessary where the ground is stone or clay, where there is insufficient percolation to allow the drainage pipes to draw off the water leaching down from the dump. Thus it is standard to install leach pipes that lead to the zero-pressure drainage tunnel, as the pressure in the surrounding stone or ground is invariably somewhat higher.